The present invention relates to radio telephone communication systems and more particularly to a method and apparatus for communicating with radio telephones when operating in a remote geographical area.
Radio or cellular telephone service is characterized by a central site transmitting through a number of distributed transmitters to a number of assigned mobile or portable radio telephones within a limited geographical area. A problem with this service is that radio telephones operating outside of the area of their assigned system (the "home system") cannot be reached through radio communication from the central site for the completion of calls. This problem has been remedied in some cases by the operators of adjacent radio telephone systems cooperating to connect their systems into a network to provide automatic radio communication coverage to radio telephones of either system throughout their combined areas of geographical coverage. Within such networks, a radio telephone operating outside of the geographical area of the home system (a "roamer"), but within the geographical area of a remote system with which the home system has combined to form a network, receives calls automatically through the remote system and communication between the home and remote systems. There is no need for the user to be aware that he or she has ventured outside the geographical area of the home system because calls are received and completed in the same manner at all locations within the network.
Briefly, in such networked systems, a call is completed to a roamer by first paging the roamer from the home system within its geographical area. If no response is received, the home system then automatically communicates with the other systems with which it is networked and requests that they conduct similar paging activity for the mobile unit within their geographical areas. If the mobile unit responds to a page from one of these other systems, the telephone call then is completed to the unit through radio communication between the unit and this other system and a telephone connection between that system and the home system.
The roamer also can be reached through a telephone port in the remote system, known as the "roamer access port," through which the remote system can be called directly. In such a system, a caller dials the telephone number assigned to the roamer access port and establishes telephone communication with the remote system. The caller then dials the ten digit telephone number assigned to the mobile u it. The remote system pages the unit, and, if the unit responds, the remote system completes the call through radio communication with the unit and through the telephone connection with the caller through the roamer access port.
Unfortunately, networking of adjacent radio telephone systems generally is feasible only if the cellular telephone equipment comprising the remote radio telephone system is made by the same manufacturer as that of the home system. At present, no standard protocol or specification exists in the cellular telephone equipment industry for networking, and, as a result, no major manufacturer's equipment is configured to automatically network with the equipment of any other major manufacturer. Thus, although virtually every principal geographical market is provided with radio telephone service, networking is not consistent.
Also, although the roamer could be called by calling the remote system directly through its roamer access port, the caller often does not know that the mobile unit has left the home system and, even if this fact is known, the caller may not know the identity of the remote system through which the mobile unit can be reached. Thus, a user of a mobile telephone has no assurance of receiving calls when he or she is in an area not served by the home system.